This invention relates to a cylinder sleeve for a two-cycle engine and more particularly to an improved port arrangement for a reciprocating machine and a method for forming such a port.
As is well known, many reciprocating machines, such as two-cycle engines, are ported. With such ported engines, separate valves are not employed but rather port openings are formed in the cylinder or cylinder liner and the movement of the piston controls the opening and closing of these port openings. Such constructions offer the ease of simplicity of the engine and relatively high power outputs. However, in order to insure good compression sealing, it is the normal practice to employ piston rings for the engine. With ported engines, on the other hand, there becomes a danger of piston rings sticking as the piston ring passes across the edge of the port opening. This problem is particularly relevant in connection with the passage of the piston ring across the top edge of the exhaust port opening as the piston approaches top dead center position. This is a point in time when the piston ring is traveling at the highest linear speed relative to the port opening and the sticking problem can occur.
A construction as shown in FIG. 1 has been proposed for reducing the sticking problem in connection with a port opening. In FIG. 1, a port opening constructed with a prior art type of arrangement is identified generally by the reference numeral 11. It will be seen that the port opening 11 is defined by a top edge 12, a pair of side edges 13 and a lower edge 14. In order to avoid piston ring sticking, the top edge 12 is curved.
As a result of this construction, piston ring sticking will be substantially reduced. However, it should be noted that the curvature of the top edge 12 causes the exhaust port to open gradually as the piston decreases. That is, the full transverse width of the port opening 11 is not opened immediately as the piston begins its movement toward bottom dead center. As a result of this, the scavenging of the engine will be adversely affected and the performance reduced.
It is, therefore, a principal object of this invention to provide an improved arrangement for the port opening of a reciprocating machine that will reduce the likelihood of piston ring sticking but at the same time will not adversely affect the port timing.
It is a further object of this invention to provide an improved exhaust port configuration for a two-cycle, internal combustion engine.
It is a further object of this invention to provide an improved method for forming a port in a reciprocating engine that will reduce the likelihood of piston ring sticking.
It is a further object of this invention to provide an improved method for forming the exhaust port opening of a two-cycle engine.